Unable to identify network traffic

[fredge]

I currently have a small NT LAN setup, with a UNIX box as a mail server.
We have a wireless LAN connection to our ISP allowing us to receive 800
MB/month. In recent weeks however, our usage per day has shot up
dramatically and we cannot find out what is causing this change. Our ISP
can only give us a usage breakdown by day, hence not allowing us to
isolate the problem further. Do you have any suggestions as to what may
be causing the problem, or how we could run a test to find out? Is there
any software we could run to analyse the situation?
Any help given would be much appreciated.
If you require further details please let me know

 

[wlipira]

I have heard of problems with the wireless technology. If someone has the information needed to connect to your network, and a wireless network card, it would be very easy to connect to your LAN while sitting in a car a block away (line of sight of course).
Have a security sweep done.
Also, use a network monitor (S.M.S. in promiscuous mode) and a performance monitor.
You should be able to identify when traffic is getting heavy on your network.
I would do a baseline of your network for a one week period, three times per day.
1. Morning
2. About lunchtime
3. Near the end of the working day.
Also, if you are using DHCP, verify what PC's are being given IP addresses.
By the way, is it entirely necessary to have a wireless connection? It, in and of itself, is a great security risk. Check the cost of a T1 line (or other technology), and see what the difference would be. It would be much more secure, and that might deter anyone from trying to access your network.
Also, read up on Wireless Technologies. I do not mean to sound rude, but you might discover many interesting things.
Also, did you have anyone get fired about the time these usage problems started?

Please let me know if any of this does help, or if you need some more information. My email to use is:

eliavrezz@mediaone.net
wlipira@mediaone.net

Regards,

Will